Cybernetic grinding



r 3,264,788 Patented Aug 9, 1966 3,264,788 CYBERNETIC GRINDING Loring Coes, In, Princeton, and Emmanuel Milias, Worcester, Mass, assignors to Norton Company, Worcester, Mass, 21 corporation of Massachusetts Filed Dec. 16, 1963, Ser. No. 330,767 Claims. (Cl. 51165) This application is a continuation-in-part of our applications entitled Grinding Machine, Serial No. 253,966, filed January 25, 1963, now Patent No. 3,167,891, issued February 2, 1965 (which, in turn, is a continuation of Serial No. 163,983, filed January 3, 1962), now abandoned.

This invention relates to grinding, and more particularly, to automatic control of grinding operations.

In Patent No. 3,167,891, there is described a number of ways of dressing a grinding wheel in response to the sensingof any of various conditions indicaing that the wheel needs to be dressed. For example, reduction in driving power, wheel speed, or in the grinding ratio, which is defined therein as the ratio of the volume of metal removed from the workpiece to the volume of material worn off the grinding Wheel during a grinding operation, may be sensed to cause a substantial change in the speed of the grinding wheel to effect dressing thereof. In that Patent No. 3,167,891 means is provided for sensing any such reduction, and such means may be employed in the equipment of the present application to provide a signal indicative of a characteristic of the grinding operation.

It is a principal object of this invention to effect automatic programming of the infeed control to regulate the infeed of the grinding wheel into the workpiece in order to remove the maximum amount of metal from the workpiece in the fastest time to produce the desired reduction in size of the workpiece with the least damage and base finish possible in accordance with the commercial aspects of the product being worked upon.

The illustrated example of this invention provides a specific embodiment in which the grinding ratio is determined and maximized in accordance with the co-pending applications, Serial Nos. 303,305, now Patent No. 3,178,861, issued April 20, 1965, and 303,306, filed in United States Patent Ofiice by the respective joint inventors of this application. Additionally, the instant workpiece dimension which is being changed is continuously electrically compared with the desired finish size of the workpiece and an output signal representing the difference factor taken. The difference factor is then multiplied by a predetermined instant slope factor which gives an output signal corresponding to a volumetric infeed rate which will optimize the infeed pattern until the difference factor is equal to or less than the tolerance factor of the workpiece. In fact, this invention provides for the taking into account of all of the necessary factors to increase the efficiency of the grinding operation by feeding these factors into a computing arrangement for maintaining the ultimate operative activity of the grinder. The invention provides for a rate of infeed that is programmed through a computer to accomplish a theoretical pattern of metal removal consistent of the planned utilization of the grinding wheel, and takes into consideration the particular properties of the metal being ground and all of the other factors controlling the grinding operation to obtain the most appropriate commercial operation.

Further objects of this invention are to provide for apparatus such as that described in the preceding paragraph. Still other objects and advantages of this invention will become apparent upon reading the appended claims and the following detailed description of the invention, in conjunction with a drawing, in which:

FIGURE 1 is a diagrammatic view indicating certain initial and instantaneous dimensions of a grinding wheel and workpiece; and

FIGURE 2 is a diagrammatic and schematic illustration of one embodiment of this invention in connection with the rapid and economical removal of metal by means of grinding with automatic control.

Several ways of making grinding operations more automatic are covered in our copending applications mentioned above. The way which this disclosure sets forth is one which may be designated as Cybernetic Grinding, in which the automatic control is governed by the amount of grinding left to be done on the particular workpiece.

For example, if the finished size of a certain workpiece is to be X and the size of the piece is at any prior instant X+AX, then the volumetric infeed rate I is equal to aAX, wherein a is a slope factor discussed above. Under such circumstances the volumetric infeed rate is highest when the amount AX of grinding to be done is greatest, and it decreases when AX approaches a constant tolerance factor b which is determined from the tolerance of the workpiece. In a plot of the infeed rate I against the amount AX of material yet to be removed, the slope factor a may be a straight line intersecting the I and AX axes at zero when a is a constant in which case a refers to the slope of the line. This invention includes not only the use of such a constant factor a, but also the use of a variable slope factor a, for example, continuously variable in order to follow any desired curve such as a parabolic, hyperbolic, exponential, or any other configuration. Regardless of variation of constancy in factor a, the invention achieves the advantages of minimizing the extent of surface injury or the depth of metallurgical burn as the workpiece approaches finished size, and at the same time the surface finish improves to the maximum attainable for the given grinding wheel being used.

As previously indicated, these advantages and objects of this invention may be accomplished by sensing various factors of the grinding operation and correlating them to cause the infeed to be such as to effect the maximum amount of metal removal in the shortest time with the desired finish.

Reference is particularly now made to the drawing wherein FIGURE 1 shows a grinding wheel 10 operating on a workpiece 112. The initial radius of the grinding wheel is designated as R, while its initial center height above surface 14 is designated as H. As the workpiece 12 is ground down, the grinding wheel itself reduces, and its instantaneous radius is designated as r. The instantaneous center height of the grinding wheel is accordingly designated h. It is therefore apparent that the workpiece height X+AX is equal to h-r. Recalling that X is the final height desired, and that AX is the amount yet to be ground off, it becomes apparent that if X is subtracted from (h-r), then the quantity AX is made known. This is exactly what is accomplished by the subtractor .16 in FIGURE 2, which receives on its left input line 18 a signal representing the quantity (h-r), and on its right hand input line 20 signal representing X. The X signal is obtained by appropriately setting arm 22 of potentiometer 24.

The instantaneous value (h-r) designating the instant height of the workpiece 12 is obtained from subtractor 26 which has an h input signal on line 28 and an r input signal on line 30. These two signals are, of course, variable during the grinding operation, and are obtained as voltages from the respective potentiometers 32 and 3 4, the movable arms '36 and 38 of which are regulated respectively in accordance with the instant Value of h and instant value of r as follows.

As indicated by arrow 40, frame element 42- which carries grinding wheel 10, is movable up and down, as

by the conventional infeed equipment fully disclosed in the aforementionedPatent No. 3,167,891 In order to sense the instant height, h, a position transducer 44 is employed. As diagrammatically indicated, its pick-up coil 46 is secured to frame element 42 so as to follow the up and. down movements thereof. Any such change in theframe element 42 causes the'output signal coil 4=6 to drive servo motor M1 through an amplifier A1.; The servo motor, in turn, drives a pinion gear 4-8, which is secured at a predetermined height by the frame element 50. Therotation of gear 48 moves rack 52 vertically so as to change the position of the transducer arma ture 54 and cause rebalance .of the transducer. Therotation of motor M1 also controls the position of potentiometer arm 36, thereby providing the voltage on line 28 which is proportionalto the instantaneous height h.

In like manner, the instantaneous wheel radius r is sensed by a transducer 56 whereby decreases in the radius of the .wheel are suppliedas a signal to the servo motor M2 through an amplifier-A2. Transducer 56 in this instance may include a magnetic or capacitance type of pick-up as indicated in the aforementioned applications.

To effect rebalance, servo motor M2 rotates pinion .gear

58 in a direction to change properly the positionof rack 60 to the lower end of which is affixed the transducer 56. In so doing, motorMZ also drives the potentiometer 7 arm 3-8 so that between it and ground there .is a voltage which is proportional to the instantaneous radius r of the grinding wheel.

Returning now to the subtractor 16, it will be recalled that the difference between the input quantities (h-r) and X p'rovides an output signal AX on line 62., This difference factor AX is multiplied by multiplier. 66 with" a factor a which appears on input line 6-4. 'The output signal aAX on line 68 from multiplier 66. is a volumetric infeed rate signal I which is applied to the grinding wheelinfeed control 74 to regulate the downfeedof grinding wheel 10, by controlling the downfeed of frame element 4 2 as indicated by dash line 76. This causes the infeed to beat such a rate that the grinding operation is optimized for the conditions desired.

It will now be explained how the factors a and b are obtained. First, it will be noted that the signal for factor a which appears on line64, comes from a programmer 70. v

The slope factor a is predetermined and will vary depending upon the characteristics of the grinding operation, especially the workpiece to be machined, suchas its initial size, strength, type of material it is made of, finish size, and the desired surface finish, etc. Once the slope factor'a is determined, .it is then putinto the programmer 70 which sends the proper signal to a multiplier 66 and the result is the proper infeed of the grinding wheel into the workpiece for the most efiicient grinding thereof.

A method of providing a slope factor a for a particular workpiece could be based on such facts, forzexample,

thatthe particular workpiece can initially withstand the grinding wheel pressure and heavy stock removal, be. cause of its size, at the beginning of the grinding cycle;

however, as the workpiece is reduced in size, it cannot take the same depth of cuts due to. its present shape, deformation and other material characteristics, or. because of some other well-proven fact. from analyzing the workpiece that the most efiicient way Finally, it is determined I toreduce the workpiece to the desired size and to provide the desired finish is to make the infeed rate 50% of" whatever stock there is left'to be removed before the desired size is reached For example, if .032 .is the.

amount AX left to be removed from the workpiece, the

first depth of cut would be .016; the second .depthof cut .008; the third depth of cut .004; the fourth depth of cut .002; the fifth depth of cut .001; the sixth depth of cut .0005, etc. until the size of the workpiece is within the acceptable tolerance which is the constant factorgb;

The slope factor a in the particular example given would be a straight line. If factor a is a curve, the depthof cut would not be a constant 50% of what stock there is left to be removed. It could be, for example, 50%, 30%, 20%, 10%, etc. of the stock remaining.

When theamount left to be removed from the work-' piece is withinthevconstant tolerance factor bcf the desired size, the grinding operation may be terminated,

leaving the :workpiece .on the-larger side of the Y desired dimension. Alternatively, theamount ofthe constant factor lrmay be fed to provide a final cut of the. workpiece which would leave the size of the workpiece on the smaller side. of the desired dimension.

The constant factor 'b "may be determined in various ways. For example, if the desired dimension of the workpiece is one inch and the tolerance plus or minus 1.001 I .o0i

.001 is used as the constant b5 is one inch, plus .005 minus 1.005. I (l.000 I X-dimension can be 1.0025 and; the tolerance .005 dividedby-two to providean equal tolerance and a constant factor bof .0025 on'either 'side of the dimension the low limit .999andbe 1.001, andthe tolerances. .003 i and .001 added together, divided bytwotoyprovide an.

equal tolerance-of pl-usor minus .002. and a constant factor b of .002.

As fully explained in the. aforementioned applications, the grinding ratio is the ratio of the. volume of the metal removed from the work piece to. the volume of material worn off the; grinding wheel during a grinding operation."

Thoseap-plications fully describe the manner in which computer 80, inresponse to the h'r subtractor 26,. delivers to output line 82; a signalwhich reflects the instantaneousa grinding ratio. In effect, the grinding ratio a is a function of the eificiency'of the grinding operation,

and the two later ones of those applications indicates that thespeed of the: grinding wheelzm aybe changed to increase and maximize. the grinding ratioand efficiency of; the operation.- In accordance therewith,-F IGURE 2 illu'strates a comparing :circuit'84 which maybe similar to that in Patent No. 3,178,861, for comparing successive values of the. grinding ratio. Asthere-in indicated, fifithe' 1 latest grinding ratio is less .than'the earlier one,'the-n the direction ofthe speed ,change'of the grinding wheel needs to be reversed, but'if it is greater; then the present speed.

changedirectionsholuldbe continued.. Accordingly, this information as determined 'by comparer: 84 isappliedto the motor speed control 86',whi'ch, in turn, regulates thespeed of thegriuding wheel via motor 88.- In this manner, the efficiency of the grinding operatiomas far aspossible from the regulation of the grinding wheel speed, is maintained at its maximum,aautomatically.

There ,-is then the furtherv desire, as effected by this invention, to increase the effi-ciencyof the grinding operation by regulating the infeed. This isl accomplished, in a the illustrated embodiment, by providing a ,slope factor a which is multiplied with AX and feeding the a=AX signal through a :normallyopen gate 78 c0ntrolled by a comparer- 96 to the grinding wheel infeed control 74 until i If? the desired dimension- AX is equal to or less than the factor b at which time the comparer 96 closes gate 78' and opens gate 94.

The factor b is obtained, for example, as a voltage determined by the setting of arm 90 on potentiometer 92. This voltage signal is applied through the gate 94 directly to the grinding wheel infeed control 74 provided the selector switch S is properly conditioned (closed) and the comparer 96 has opened the gate 94.

Therefore, it is apparent that the grinding wheel infeed control 74 is operated at a rate in accordance with the factor a: and AX, the amount of material left to be machined off the workpiece. The latter is only until AX decreases to or less than the value of factor b, at which time the comparer signal gate 78 is closed preventing further infeed (I=aAX) from the multiplier 66 and opens the gate 94 which provides a way of feeding the factor b, if desired, i.e., if switch S is closed.

The equipment for selecting and effecting a cut equal to b includes the aforesaid selector switch S and comparer 96, which receives the factors AX and b respectively on lines 98 and 100. The gate 94 is normally closed, but when AX decreases to or less than the value of b, then the comparer opens the gate 94 allowing signal b to pass through the switch S to the grinding wheel infeed control 74. Automatically, only one cut is accomplished when gate 94 so opens. one cut is made the last out in any desirable manner. For example, the comparer output to gate 94 may be made just a .pulse to trigger control 74 once, or that output may be timed in comparer 96 to end at the proper time. Alternatively, control 74 may be constructed to accomplish the desired end by receiving any sort of signal on its input line 106.

As soon as the last cut is made, the grinding wheel infeed control 74 is cutoff by the co-mparer 96. To recycle, the programmer is reset, in any suitable manner such as by the removal or insertion of another workpiece in the machine.

The exemplary embodiment of this invention above described is intended to be illustrative of a system which employs a predetermined constant factor a. However, as previously indicated, the factor a may be variable in accordance with any number of desired characteristics which indicate various etficiencies or the like in the grinding operation, such as the final characteristics desired for the final product.

It is therefore apparent that this invention has provided for the objects and advantages herein stated. Other objects and advantages, and even further modification of the invention, will become apparent to those of ordinary skill in the art upon reading this disclosure. However, it is to be understood that this disclosure is illustrative of the invention defined by the scope of the following claims.

What is claimed is:

1. Apparatus for automatically increasing the efliciency of a grinding operation by a grinding wheel on a work piece, comprising:

means for determining the difference factor AX between the instant size of said work piece and a desired size thereof, and

means for computing an infeed I equal to a function of AX, wherein I is less than AX.

2. Apparatus for automatically increasing the efiiciency of a grinding operation by a grinding wheel on a work piece, comprising:

means for determining the difference factor AX between the instant size of said work piece and a desired size thereof,

means for providing a factor a relating to at least one characteristic of said grinding operation including said workpiece,

means for combining said factors to determine and provide infeed rate signal I equal to aAX, and

means responsive to said signal I for controlling the relative infeed of said grinding wheel and work piece.

3. Apparatus as in claim 2 and further including means for providing a factor b relating to the allowable tolerance of said desired size of said work piece, and

means for providing a given output signal when factor AX becomes equal to or less than factor b to terminate grinding of the Work piece. 4. Apparatus as in claim 2 and further including means for continuously determining when the factor AX decreases to a value equal to or less than factor b for providing a predetermined output signal, and

means responsive to that signal causing said infeed rate signal I then to be equal to b and the final cut by said grinding wheel of said work piece.

5. Apparatus for automatically increasing the efficiency of a grinding operation by a grinding wheel on a work piece, comprising:

means for determining the difference factor AX between the instant size of said Work piece and a desired size thereof,

means for providing a predetermined slope factor a,

means for providing a factor b relating to the allowable tolerance of said desired size, means including a multiplier for multiplying the factor a by AX to determine an infeed rate signal 1,

means responsive to said signal I for controlling the relative infeed of said grinding wheel and work piece,

means for providing a predetermined output signal when AX becomes less than or equal to b,

means responsive to said given signal for causing the said infeed rate signal I then to be equal to b, and

means in said infeed controlling means responsive to said given signal for stopping the grinding action following the final cut determined by the last mentioned infeed rate signal.

6. Apparatus for automatically increasing the efficiency of a grinding operation by a grinding wheel on a work piece, comprising:

means for determining the difference factor AX between the instant size of said work piece and a desired size thereof,

means for providing a factor a relating to at least one characteristic of the grinding operation including said work piece,

means for combining said factors to determine aninfeed rate signal I equal to aAX, means for providing a factor signal b relating to the allowable tolerance of said desired size, and

means responsive to said signals I and b for controlling the relative infeed of said grinding wheel and work piece.

7. Apparatus as in claim 6 and further including means for providing a given output signal when AX becomes less than b, and

means responsive to said output signal for causing the said infeed rate signal to be terminated.

8. Apparatus as in claim 6 and further including means for computing the grinding ratio of said grinding operation, and

means responsive to the output of said grinding ratio computing means for controlling the speed of said grinding wheel to maximize the grinding ratio and increase the efficiency of said grinding operation.

9. Apparatus as in claim 8 and further including means for continuously determining when the factor AX decreases to the value of factor b for providing a predetermined output signal, and

means responsive to that signal for causing the final cut to be made by said grinding wheel on said work piece.

10. Apparatus for automatically increasing the efiicieucy of a grinding operation by a grinding wheel on a work piece, comprising:

means for determining the difference factor AX between the instant size of said work piece and a desired size thereof,

meansf0r continuously computing the grinding ratio of said grinding operation,

meansresponsive to the output ofsaid computing means for controlling the speed of said grinding Wheelto cause the grinding ratio to increase and maximize, means for providing a factor b relating to the allowable tolerance of said desired size,

means including a multiplierfor multiplying a predeterrt mined slope factor a by AX to determine an infeed rate signal I,

means responsive to said signalvI for :controlling they 9 relative infeed of said grinding Wheel andwork piece, means for providing a predetermined output signal 5 when AX becomes less than b, and; means responsive to said output signal forcausing the saidfactor b.

References:- Cited by the Examiner UNITED 1 STATES PATENTS Conradson et a1. 5l16'5 Xi Schultze; et a1 5l' v165 Morgan et a1. 51 165 Z Coes-etalp 51165- Milias 51-165 LESTER SWINGLE, Primary Exrzmir er; 

1. APPARATUS FOR AUTOMATICALLY INCREASING THE EFFICIENCY OF A GRINDING OPERATION BY A GRINDING WHEEL ON A WORK PIECE, COMPRISING: MEANS FOR DETERMINING THE DIFFERENCE FACTOR $X BETWEEN THE INSTANT SIZE OF SAID WORK PIECE AND A DESIRED SIZE THEREOF, AND 